The majority of technically available epoxy resins are obtained by the conversion of polyphenols with epichlorohydrin (ECH). The glycidyl compounds that thereby arise comprise, according to the conditions of the process, some tenths of a percent of chemically bound chlorine. Chlorine-free epoxy resins are preferable for various reasons, including ecological ones, and appear to be manufacturable via ECH synthesis, if at all, only with a large capital outlay and thus at a high cost.
However, halogen-free epoxy resins are of interest in particular for electronics applications, where the aim is to realize freedom from corrosion under temperature, climate and tensile stress.
In addition, resin components are desirable whose molar mass can be adjusted easily, preferably in the direction of higher-molecular products, by means of corresponding process parameters, in order in this way advantageously to construct flow and shrinkage behavior of formulations constructed therefrom.
Epoxy resins of this sort are required in particular for cationic hardening. In addition, given other hardening mechanisms they can also replace chlorine-containing polyepoxies, which are currently an essential component of molding compounds and circuit board materials.
Manufacturing methods are known that are based at least on halogen-free initial components. For example, ring-epoxied cycloaliphatic epoxy resins with polyphenols are converted to high-viscosity to solid epoxy resins. However, a considerable portion of halogen is introduced by the catalysts used, such as for example ammonium halide and phosphonium halide, since these catalysts can no longer be removed completely after the reaction has taken place. These catalyst residues are in addition responsible for the limited storage stability of epoxy resins synthesized in this way.
Another way, using epoxization of allyl-functional aromates by means of peracetic acid, failed due to the safety risk posed by this manufacturing process.